Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-09-24
2001-10-09
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06300995
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device for driving a liquid crystal by means of an in-plane-switching system to apply an electric field which is almost parallel to a substrate between a picture element electrode and counter electrode.
An active matrix type liquid crystal display device using an active component, such as a thin film transistor (TFT), is widely used as a display, having such characteristics as being thin and light weight, and having a high displaying quality. A liquid crystal display device of this type is constructed with a liquid crystal provided between an active matrix substrate having a TFT element and an opposite substrate, and an electric field is applied between picture element electrodes and a counter electrode so as to drive and control the liquid crystal, whereby light incident on the liquid crystal is modulated so as to form an image.
Further, in order to widen the viewing angle of a liquid crystal display device, a liquid crystal display device using an in-plane-switching system has been proposed, in which the picture element electrode and the counter electrode are formed on the active matrix substrate, and an electric field is applied in parallel to the surface of the substrate. Such a device is described, for example, in Proceedings of the 15th International Display Research Conference, p. 707 (1995) or Japanese Patent Laid-open 7-36058 Bretin. The in-plane-switching system has the advantage of being able to provide a wide visual angle, because the liquid crystal is controlled by an electric field applied in a substantially transverse direction relative to the viewing angle.
The conventional display device using in-plane-switching has a configuration in which metal films, formed under a protective insulation film, serve as the picture element electrodes and the counter electrodes thereto. However, since the electric field is applied to the liquid crystal through the protective insulation film, an electrical voltage loss occurs, with the result that the driving voltage becomes large, causing a problem in that the power consumption increases. Moreover, while it is effective to make the spacing between the picture element electrodes and the counter electrodes big in order to enlarge the aperture ratio, this requires the driving voltage to be even larger. Since the threshold driving voltage of the liquid crystal is restricted by the upper limit of the driving voltage, there arises a problem in that the selection of a liquid crystal which has a fast responsiveness is limited.
Such an increase in the power consumption caused by such an electrical voltage loss may be avoided by providing a contact hole which forms an aperture in the gating isolation film and by providing an electrode for driving the liquid crystal through this aperture, as described in Japanese Patent Laid-open No. issue 7-128683 bulletin. However, the usual metal electrode has a problem in that it is corroded by the liquid crystal composition, so that it is necessary to form a protective insulation film on top of the electrodes. Naturally, in this case, the electrical voltage loss which occurs due to the protective insulation film increases even more.
SUMMARY OF THE INVENTION
An object of the present invention is to reduce losses in the driving voltage applied to the liquid crystal, by providing an active matrix substrate in which degradation of the metal electrode is prevented in a liquid crystal display device.
In the liquid crystal display device of the present invention, plural gate electric wiring, plural drain electric wiring intersecting therewith in a matrix state, plural thin film transistors formed opposite to each intersection of the gate and drain electric wiring, and plural common electric wiring extending in the same direction as the gate electric wiring are provided on one of a pair of substrates. At least one picture element is formed in each field surrounded by the plural gate electric wirings and the drain electric wirings, said each picture element having a counter electrode extending in the same direction as the drain electric wiring, connected to the common electric wiring corresponding to each picture element, and a picture element electrode extending in the same direction as the counter electrode connected to the thin film transistor corresponding to each picture element. By an electrical voltage applied between said counter electrode and said picture element electrodes, an electric field is generated that has a parallel component mainly opposite to said one substrate in the liquid crystal layer. The counter electrode contacts the liquid crystal layer directly.
According to an embodiment of the present invention, the insulator layer is formed on top of the common electric wiring, and the counter electrode is connected with the common electric wiring through the contact hole formed by this insulator layer. The insulator layer consists of a first insulator layer and a second insulator layer, the first insulator layer being formed on the gate electric wiring and the common electric wiring, and the second insulator layer being formed on the drain electric wiring and the plural thin film transistors.
Moreover, the source electrode of each thin film transistor is formed on the first insulator layer and serves as the picture element electrode. Furthermore, the source electrode may be connected to the picture element electrode through the contact hole formed by the second insulator layer mentioned above. In this case, the picture element electrode contacts the liquid crystal layer directly, the counter electrode. It is preferable that the counter electrode or the picture element electrode consists of a conductive oxide film or graphite.
According to another embodiment of the present invention, a drain electric wiring terminal and a gate electric wiring terminal, in which the drain electric wiring and the gate electric wiring are connected to the drive circuitry, are constructed with the conductive oxide film or the graphite.
REFERENCES:
patent: 4345249 (1982-08-01), Togashi
patent: 5576867 (1996-11-01), Baur et al.
patent: 5598285 (1997-01-01), Kondo et al.
patent: 5841498 (1998-11-01), Baur et al.
patent: 5886762 (1999-03-01), Yamazaki et al.
patent: 5892562 (1999-04-01), Lee et al.
Ando Masahiko
Fukaya Ritsuo
Wakagi Masatoshi
Antonelli Terry Stout & Kraus LLP
Hitachi Ltd
Parker Kenneth
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